The present invention relates to a process for fabrication of conductive oxides as electrodes for electrochemical capacitors. The process has the features of low cost, easy setup, low processing temperature, and coating on irregular surface. The conductive oxides have the feature of controllable surface area and electrical properties.
The traditional electrode materials for electrochemical capacitors are high surface area carbon, metal oxides, and conducting polymers. Ruthenium oxide (RuO2) has been identified as one of the best materials for this purpose.
Several deposition techniques have been used to prepare RuO2 films. These techniques include reactive sputtering, metalorganic chemical vapor deposition (MOCVD), pulsed laser deposition, low-temperature chemical vapor deposition, and oxygen plasma-assisted molecular beam epitaxy. These methods tend to produce dense RuO2 films that have small surface area and exhibit low power storage density. Recently, the hydrous form of ruthenium oxide (RuO2.xH2O) with amorphous structure has been demonstrated to be an electrode material for electrochemical capacitors (see, Zheng et al., J. Electrochem. Soc., 142, L6 (1995) and U.S. Pat. No. 6,097,588). Ruthenium oxides for electrochemical capacitors are also described in U.S. Pat. No. 5,600,535, U.S. Pat. No. 6,025,020, and U.S. Pat. No. 6,133,159.
A similar thin film growth technique used to grow RuO2 at higher temperatures of greater than 500xc2x0 C. was described in pending patent application of Jia et al., Ser. No. 09/629,116, filed Jul. 20, 2000 for xe2x80x9cPolymer-assisted Aqueous Deposition of Metal Oxide Filmsxe2x80x9d.
It is an object of the present invention to provide a process for preparation of conductive metal oxide films.
It is a further object of the invention to provide a process for preparation of such conductive metal oxide films with controllably increased surface area.
It is a still further object of the invention to provide a process for preparation of such conductive metal oxide films with controllable electrical properties.
In accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a process for the preparation of a metallic oxide composite including mixing an aqueous solution of a water-soluble metal compound and colloidal silica, depositing said mixture upon a substrate, heating the mixture-coated substrates at temperatures from about 150xc2x0 C. to about 300xc2x0 C. for time sufficient to form a metallic oxide film, and, removing said silica from said metallic oxide film whereby a porous metal oxide structure is formed.
The present invention further provides a composition of matter including a composite metal oxide film containing a conductive metal oxide in admixture with silica particles.